According to IMDB, approximately: 130
Including his past kills, and the growth of his slide collection between seasons, Dexter has killed (at the very least) 100 people: around 55 of these have been on-screen kills (including flashbacks). In S5E1 he claims to have killed 67 deserving people, though if the 12 inbetween S3 and S4 is taken into account (portrayed in the Turned Upside Down promo), this should actually be around 88 at the start of season 5.
In S2E8 Dexter’s slide box is revealed to have 46 slides in it. Taking into consideration all the on-screen slide kills from S1E1 (including flashbacks) till then, there are 32 slides unaccounted for (though at least 18 are identified during the BHB investigation). It is established that Dexter has killed before he began to take trophies (First Nurse, Juan Rinez,), which brings Dexter’s potential pre-series kill total to 36 (this includes Early Cuts characters Peter Thorton and Robert Milson). So, 130ish…
You want a break down?
Here we go… Victim – Death
- Mike Donovan – Power Saw
- Jamie Jaworski – Meat Cleaver
- Matt Chambers – Knife to the Heart
- Nurse Mary – Knife to the Heart
- Jorge Castillo – Knife
- Valerie Castillo – Knife to Carotid Artery
- Alex Timmons – Unknown
- Gene Marshall – Unknown
- Cindy Landon – Unknown
- Dr. Emmett Meridian – Power Saw
- Brian Moser (The Ice Truck Killer) – Slit Throat
- Little Chino – Knife to the Heart
- 18 Previously Unmentioned Victims Uncovered as BHB Victims
- Roger Hicks – Knife to the Heart
- Ken Olsen – Beheaded with a Cleaver
- Santos Jiminez – Chainsaw
- More Unmentioned Blood Slide Victims
- Jose Garza – Hand Saw
- Juan Rinez – Unknown
- Esteban Famosa – Snapped his Neck
- Teo Famosa – Shot
- Lila West – Knife to the Heart
- Unnamed Carnival Attendant – Meat Cleaver
- Oscar Prado – Knife to the Heart
- New Slide Box with 4 More Slides
- Fred “Freebo” Bowman – Knife to the Neck
- Nathan Marten – Strangled
- Ethan Turner – Knife to the Heart
- Clemson Galt – Knife to the Heart
- Camilla Figg – Poisoned Keylime Pie
- Miguel Prado – Garotted
- George Washington King (The Skinner) – Broke Neck
- Benito Gomez – Knife to the Heart
- 12 More Unmentioned Victims in Slide Box
- Zoey Kruger – Knife to the Heart
- Jonathan Farrow – Decapitated with Cleaver
- Stan Beaudry – Throat Ravaged with Power Saw
- Arthur Mitchell – Bludgeoned with Hammer
- Rankin – Beaten to Death
- Boyd Fowler – Stabbed in Heart
- Dan Mendell – Neck Snapped
- Lance Robinson – Strangled
- Cole Harmon – Stabbed in Heart
- Alex Tilden – Stabbed
- Stan Liddy – Stabbed in Heart
- Ben – Killed with Defibrillator
- Roger – Killed with Defibrillator
- Joe Walker – Hit in Head with Hammer and Stabbed in Chest
- 12 More Unmentioned Slides in Box
- Julio Benes – Throat Slit
- Walter Kenney – Suffocated with Pillow
- Nick – Drowned
- Norm – Stabbed with Pitch Fork
- Steve Dorsey – Stabbed in Stomach
- Beth Dorsey – Trapped by Gas Bomb
- Alberto – Stabbed with Harpoon
- Travis Marshal – Stabbed in Chest
- Viktor Baskov – Bludgeoned with Fire Extinguisher
- Ray Speltzer – Stabbed with a Stake
- Unknown Hitman – Throat Slit
- Oleg Mickic – Stabbed in the Back
- Clint Mckay – Stabbed in the Chest and Thrown Overboard
- Hector Estrada – Stabbed in the Heart and Shot
- Unknown – Power Tool
- Andrew Briggs – Stabbed in Chest
- Ron Galuzzo – Stabbed in Chest
- A.J. Yates – Impaled with Curtain Pole through Bed
- Oliver Saxon – Stabbed in Throat with a Pen
- And sadly, Debra Morgan – Turned off Life Support